The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
It is generally known that in a hybrid drive a superimposed transmission constructed in planetary design can be used for superimposing the torques and speeds of a combustion engine or an electric machine. Compared with other construction types of superimposed transmissions, a planetary transmission has the advantage that the transmission components have compact measurements and adjusted bearing forces.
DE 199 34 696 A1 describes a combination of a combustion engine, an electric machine and a superimposed transmission depicted as an electrodynamic drive system (EDA), which precedes a gearbox in countershaft design and allows for an abrasion-free start. According to FIG. 1 of the above-mentioned patent specification, a first embodiment of this hybrid drive shows that the superimposed transmission is designed in the form of a simple planetary transmission with a sun wheel, a planet carrier supporting multiple planetary gears and a ring gear. The ring gear of the planetary transmission is connected non-rotatably to the drive shaft of the combustion engine and forms the first input element of the superimposed transmission. The sun wheel of the planetary transmission is connected non-rotatably to the rotor of the electric machine and forms the second input element of the superimposed transmission. The planet carrier of the planetary transmission is connected non-rotatably to the input shaft of the gearbox and forms the output element of the superimposed transmission.
In this hybrid drive, the abrasion-free start occurs in that the combustion engine maintains a mostly constant speed and the electric machine is first controlled in generator operation with increasing drag torque until the rotor reaches a standstill and then accelerated in engine operation with opposite direction of rotation until the transmission components of the planetary transmission achieve synchronized movement. When a synchronized movement in the planetary transmission is achieved, a lock-up clutch situated between the sun wheel and the planet carrier is closed so that during further combustion operation the planetary transmission revolves in the block. In this operating condition, the electric machine can be run as a motor for a boost operation, operated as a generator for charging an electric energy storage device or switched powerless. When the drive shaft of the combustion engine is connected to the ring gear of the planetary transmission via a decoupler which can be engaged and disengaged, the combustion engine can also be disconnected and shut off to allow for pure electric drive. Without changing anything, the gearbox of this hybrid drive can also be used for a conventional drive, in which a start with the combustion engine takes place wear-prone via the slip operation of a decoupler designed in the form of a friction clutch.
DE 10 2010 030 567 A1 and DE 10 2010 043 354 A1 describe hybrid drives in which a respective gearbox in countershaft design, which is combined for drive-connecting an electric machine to a superimposed transmission constructed in planetary design, is specifically configured for use in a hybrid drive. Therefore, the respective gearbox cannot be modified with only a few changes to be used in a conventional drive train nor can it be derived therefrom. Therefore, its development and production are comparatively expensive.
In a first version of the hybrid drive described in DE 10 2010 030 567 A1, according to FIG. 1, the two input shafts are arranged coaxially and axially adjacent to one another and can be connected with one another non-rotatably via a coupling-switching element. The first input shaft is connected via a decoupler designed in the form of a friction clutch to the drive shaft of the combustion engine and can be connected via a switchable spur gear stage to the output shaft. The superimposed transmission designed in the form of a simple planetary transmission is arranged coaxially and axially adjacent to the second input shaft. Therefore, the ring gear of the planetary transmission forms the first input element of the superimposed transmission. The sun wheel of the planetary transmission is connected non-rotatably to the rotor of the electric machine and therefore forms the second input element of the superimposed transmission. Via a bridging contact member, the planet carrier of the planetary transmission can be connected non-rotatably to the second input shaft of the gearbox and via a further switchable spur gear stage, it can be connected to the output shaft. As a result, the planet carrier of the planetary transmission forms the output element of the superimposed transmission.
Besides the possibility for an abrasion-free start, this well-known hybrid drive has three gears for combustion operation and two gears for electric drive. In addition, there is the possibility of independently charging an electric energy storage device by means of the combustion engine, as well as the ability of starting the motor of the combustion engine by means of the electric machine. However, this hybrid drive has the disadvantage of having only a small number of gear steps available in the combustion operation and low transmission efficiency in the electric drive resulting from the drag losses of the spur gear stages.
In the hybrid drive according to DE 10 2010 043 354 A1, the superimposed transmission designed in the form of a simple planetary transmission is arranged within the gearbox in countershaft design, which has two input shafts and one output shaft. The first input shaft of the gearbox is arranged axially parallel to the output shaft, connected to the drive shaft of the combustion engine via a decoupler designed in the form of a friction clutch, and can be connected to the output shaft of the gearbox via two spur gear stages respectively consisting of idlers. The second input shaft of the gearbox is arranged axially parallel to the first input shaft and output shaft, connected non-rotatably to the rotor of the electric machine, and can be connected to the output shaft of the gearbox via two spur gear stages also respectively consisting only of idlers. The spur gear stages of the first input shaft and the second input shaft are arranged in identical, or almost identical, gear levels and utilize in the one case a mutual idler which is arranged on the output shaft. In the other case, the idlers of the two spur gear stages arranged on the output shaft are connected with one another in a rotationally fixed manner. The superimposed transmission designed in the form of a simple planetary transmission is arranged coaxially with the output shaft between the two gear levels. The ring gear of the planetary transmission is connected non-rotatably to the two idlers of the first gear level, which are also connected with one another in a rotationally fixed manner. Via a respective switching device, said idlers can be connected to the first input shaft or the second input shaft, and via a further switching device they can be connected non-rotatably directly to the output shaft. As a result, the ring gear of the planetary transmission can form the first input element or the second input element of the superimposed transmission. By means of a switching device, the sun wheel of the planter transmission can be connected non-rotatably to the mutual idler of the second gear level, which idler, in turn, can be connected via a respective switching device to the first input shaft or the second input shaft, and via a further switching device, it can be connected non-rotatably directly to the output shaft. Therefore, the sun wheel of the planetary transmission can also form the first input element or the second input element of the superimposed transmission. The planet carrier is connected non-rotatably to the output shaft and, accordingly, forms the output element of the superimposed transmission.
Besides the possibility for an abrasion-free start, this well-known hybrid drive has seven gears for combustion operation, including four winding gears, and seven gears for electric drive, also including four winding gears. This hybrid drive also involves the possibility of independently charging an electric energy storage device by means of the combustion engine and the possibility of starting the motor of the combustion engine by means of the electric machine. However, this hybrid drive has the disadvantage of having a large number of required switching devices, a large number of switching devices to be engaged and disengaged for most of the gears, and poor transmission efficiency in the winding gears.
On the other hand, in the non-prepublished patent DE 10 2013 215 114 A, the same applicant proposes several embodiments of a hybrid drive of the design mentioned above, which have a gearbox in countershaft design and a superimposed transmission in planetary design. Said hybrid drive has a large number of gears for combustion operation and two gears with high transmission efficiency for electric drive, and it has a gearbox which can be derived with a few modifications from a conventional gearbox.
In this well-known hybrid drive, the superimposed transmission is arranged coaxially with a free end of an output shaft of the gearbox. A first input element of the superimposed transmission is connected non-rotatably to a hollow shaft which is arranged coaxially with the output shaft. Via a coupling-switching element, said hollow shaft can be connected non-rotatably to an idler of an axially directly adjacent spur gear stage of the gearbox in order to couple the combustion engine. For bridging the superimposed transmission, it is possible via a bridging contact member to connect non-rotatably the hollow shaft to a further transmission component of the superimposed transmission. For shifting a second gear step for the electric drive, the hollow shaft is fixed at the housing via a switching device. A second input element of the superimposed transmission is permanently drive connected to a rotor of the electric machine, and the output element of the superimposed transmission is connected non-rotatably to the output shaft of the gearbox.